A battery-powered acoustic device intended to compensate for impaired hearing by transmitting amplified sound waves to the eardrum through air. It typically consists of a miniature microphone, amplifier, and speaker (receiver) in a case that fits the ear canal [in-the-canal (ITC)] or in a case nearly hidden in the ear canal [completely-in-the-canal (CIC)]. The microphone receives sound waves and converts them into electrical signals which are increased by the amplifier and sent as sound waves, by the speaker, to the eardrum. It is used for mild to moderately-severe hearing loss; most types are programmable to enable computerized adjustments for a patient's hearing loss and related factors.